Treating motor fuels



Patented Aug. 26, 1941 TREATING MOTOR FUELS Forrest L. McKennon,Galveston. Tex., assignor to Pan American Refining Corporation, NewYork, N. Y., a. corporation of Delaware No Drawing. Application December15,1939,

Serial No. 309,347. I e

.This invention .relates to the treatment of hydrocarbon liquids andparticularly to the removal of lmercaptansfrom petroleum distillatescontaining thesame in solution.

Petroleum distillates, especially distillates withinthegasoline boilingrange, obtained by straight distillation or by cracking are not usuallysu'i'tableIfor useas motor fuels without purification. .Among theundesirable substances present in petroleumdistillates are sulfur andits derivatives. .Sulfur occurs in petroleum distillates in manydifferent forms, a small proportion occurringin the elemental state, anda comparatively large proportion occurring as hydrogen sulfide, and inthe. form-of organic derivatives of sulfur. Thelatterare of two types,acidic and neutral. Ifhe acidic type includes mercaptans which, togetherwith hydrogen sulfide, are responsible for theunpleasant odor ofunrefined petroleum distillates of the gasoline boiling range.

The malodor of unrefined distillates can be removed by the so-calleddoctor sweetening in which the distillates are treated with a sodiumplumbite solution to convert the mercaptans to lead mercaptides, and thelatter subsequently oxidized to disulfides by the addition of sulfur.While this method is effective in producing a sweet distillate it hasthe disadvantage of reducing the knock rating of the motor fuel as wellas its so-called lead susceptibility. or response to the addition oflead tetraethyl.

It is therefore an object of the present invention to provide animproved method of removing acidic organic compounds such as mercaptansfrom petroleum distillates. Another object of the invention is toprovide an improved method of removing mercaptans and other acidicorganic substances from petroleum distillates without decreasing theknock rating of such distillates. A further object of the invention isto provide an improved method of sweetening petroleum distillateswithout affecting the lead susceptibility of the distillates toward leadtetraethyl. Other objects and advantages of the invention will becomeapparent as the description thereof proceeds.

I have discovered that the foraging objects can be attained by treatingmotor fuel distillates containing mercaptans with an aqueous causticsOlution containing urea, or a substituted urea,

and preferably a saturated solution of an urea in a.10% (by Weight)aqueous solution of sodium or potassium hydroxide. Specific examples ofureas we may employ are: urea, butyl urea, diacty'l urea, diethyldiphenyl urea, phenyl urea, mono-o-tolyl urea, diamyl urea, triethylurea, tetra. propyl urea and other symmetrical and unsymmetricalsubstituted ureas. The concentration of the aqueous caustic alkali mayvary within wide limits. However, I prefer to use solutions which areabove about 2 normal and preferably between 4 and 10 normal. .Althoughit is preferred to use a saturated solution of the urea, concentrationsof from about 1 gram per liter to about 1,000 grams per liter may beemployed.

The. amount of aqueous alkali solution employed in the extraction ispreferably above about 5% by volume and preferably from about 10% toabout by volume. It is possible to employ by volume of the-aqueoussolution, buteconomicallythis is not desirable.

Removal of the mercaptans from the petroleum distillates may be carriedout by mixing the distillate with a predetermined amount of the aqueouscaustic alkali solution containing the urea and separating the aqueouslayer containing the removed mercaptans from the upper oily layer whichis substantially free of the undesirable sulfur compounds. The treatmentmay be carried out at temperatures between about 32 F. and about F.although it is preferred to use treating temperatures of from about 60F. to about 80 F. If the desired reduction in mercaptan content is notobtained by a single extraction, additional improvement may be obtainedby extraction in a multi-stage extraction system.

The following test illustrates the effectiveness of my invention inremoving mercaptans from a petroleum distillate containing the same. Inall of the tests the petroleum distillates Were extracted once withsaturated solutions of urea in 10% (by weight) aqueous sodium andpotassium hydroxide solutions at a: temperature of about 80F. Volumeratios of about five parts of petroleum distillate to about one part ofthe alkali solutions were employed. The results obtained are summarizedin the following table:

The efiectiveness of the presence of urea in aqueous alkali solutions inremoving mercaptans from petroleum distillates is strikinglydemonstrated by the above data.

While I have employed strong bases such as aqueous solutions of sodiumand potassium hydroxide various other bases may be used, such asammonia, the alkaline earth hydroxides, the alkali metal carbonates andothers.

The mercaptans extracted from the petroleum distillate by the aqueouscaustic solutions may be recovered from the spent caustic by heating thesame to its boiling point and blowing with steam. The mixture of steamand mercaptans is condensed and the layers of mercaptans and.

water separated.

The herein described method is not necessarily limited to the removal ofmercaptans from petroleum distillates. It is equally adaptable to theremoval of other organic relatively weak acid reacting substances suchas phenols, thiophenols, fatty acids and the like from weakly basic orneutral organic liquids which are immiscible with water.

Having fully described my invention what I claim as new and desire tosecure by Letters Patent is:

1. The method of removing acid reacting materials from a hydrocarbonliquid containing the same, comprising treating the liquid with anaqueous solution of a strong base containing a substantial amount of anurea dissolved therein under conditions conducive to the extraction ofthe acid reacting materials from the hydrocarbon liquid, and separatingthe aqueous solution containing the extracted acid reacting materialsfrom the hydrocarbon liquid substantially free of the undesired acidreacting materials.

2. The method described in claim 1 in which the aqueous solution is a 2to 10 normal alkali metal hydroxide solution.

3. The method of removing mercaptans rrom a hydrocarbon distillatecontaining the same, comprising contacting the hydrocarbon distillatewith an aqueous solution of a strong base containing a substantialamount of an urea, separating the mixture into an upper layer comprisingsubstantially the hydrocarbon distillate substantially free ofmercaptans and a lower aqueous solution containing dissolved therein theundesired mercaptans.

4. The method of removing mercaptans from a hydrocarbon motor fueldistillate comprising extracting the distillate with about a 10% toabout a by volume of an aqueous solution of about 2 to about 10 normalalkali metal hydroxide saturated with urea, under conditions to form twolayers, an upper layer comprising the hydrocarbon motor fuel distillatesubstantially free of mercaptans and a lower aqueous layer containingthe undesired mercaptans.

5. The method of preparing a substantially sweet motor fuel distillatecomprising extracting a sour motor fuel distillate with a saturatedsolution of urea in a 10% by weight aqueous solution of an alkali metalhydroxide at a temperature from about F. to about F. and subsequentlyremoving the motor fuel distillate substantially free of mercaptans fromthe aqueous solution of alkali metal hydroxides saturated with urea andcontaining a substantial amount of the undesired mercaptans.

FORREST L. McKENNON.

